2018-03-16 : If a creature can't attack for any reason (such as being tapped or having come under that player's control that turn), then it doesn't attack. If there's a cost associated with having a creature attack, the player isn't forced to pay that cost, so it doesn't have to attack in that case either.

2018-03-16 : The controller of each attacking creature still chooses which player or planeswalker that creature attacks.